Converting int account IDs to str in DBT Cloud connections

[amoghrajesh]

While working on #51930, realised another thing: we define login as "str | None" and define those as str for DBT cloud connection type. If that's the case, the connection can never be converted to a uri and fails like so:

ERROR providers/dbt/cloud/tests/unit/dbt/cloud/hooks/test_dbt.py::TestDbtCloudHook::test_trigger_job_run_with_retry_from_failure[get_job_runs_data1-False-explicit_account] - TypeError: quote_from_bytes() expected bytes

Hence, instead of modifying the login type in connection model, we should convert that to string while creating the DBT connections. A later follow up can be actually taking input as a string in the hook.

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